Attempting to fix #954

This fixes the handling of readonly public properties by unsetting them and thus making them available for intercept by the magic methods. Cloning, serialization and deserialization are handled accordingly.

When instantiating a proxy object, the readonly properties are unset from the scope of the proxy parent class, allowing them to be initialized by the proxy factory and, later, the persister.

This paves the way to allow lazy loading in the presence of readonly public properties.

To fully support readonly public properties, the ProxyFactory cloner implementation and the UnitOfWork createEntity method must account for them, avoiding repeat initializations.